CGAL users discussion list

[Zhanghong Tang <>]

Hi Guillaume,

Thank you very much for your kindly reply. Now I have the following code to unite many objects into one:

typedef struct object
{
    void *obj;
}myobj;

void UnionObject(myobj *object, void *unionobj, int nobject)
{
    Polyhedron obj, UnitedObj;
    Nef_polyhedron nef_uni;
    for (int i=0;i<nobject;i++)
    {
        obj=*(Polyhedron *)object[i].obj;
        Nef_polyhedron nef_obj(obj);
        if(i==0)
            nef_uni = nef_obj;
        else
            nef_uni = nef_uni + nef_obj;

    }
    nef_uni.convert_to_polyhedron(UnitedObj);
}

However, the program crash in the line
Nef_polyhedron nef_obj(obj);

Is there any missing to do this? How to modify the code to let the multiple objects be united correctly?

I checked the polyhedron obj of every object[i].obj and output them to OFF file and they are all correct (under Guillaume's help).

Thanks

---

From:
To:
Subject: RE: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?
Date: Wed, 25 Jan 2012 14:00:22 +1200

Hi Guillaume,

Thank you very much for your kindly reply. Now I have the following code to unite many objects into one:

typedef struct object
{
    void *obj;
}myobj;

void UnionObject(myobj *object, void *unionobj, int nobject)
{
    Polyhedron obj, UnitedObj;
    Nef_polyhedron nef_uni;
    for (int i=0;i<nobject;i++)
    {
        obj=*(Polyhedron *)object[i].obj;
        Nef_polyhedron nef_obj(obj);
        if(i==0)
            nef_uni = nef_obj;
        else
            nef_uni = nef_uni + nef_obj;

    }
    nef_uni.convert_to_polyhedron(UnitedObj);
}

However, the program crash in the line
Nef_polyhedron nef_obj(obj);

Is there any missing to do this?
I checked the polyhedron obj of every object[i].obj and output them to OFF file and they are all correct (under Guillaume's help).

Thanks

---

Date: Tue, 24 Jan 2012 10:20:05 +0100
From:
To:
Subject: Re: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?

Hi,

Hi Guillaume,

Thank you very much for your encouragement. I don't understand the benefit to wirte like this: the very complex class, constructor, and so on.

The benefit is genericity.

Is it possible to write just what need to be executed, or the process of execute can be see naturaly. For example:

the function:

Polyhedron Build_triangle(int nVertices0, double *Vertices0, int nTri0, int *Tri0)
{
...
}

the caller:
...
Polyhedron P;
P=Build_triangle(nVertices,Vertices,nTri,Tri);

No this is not possible: you have to use the format required by the incremental builder class...

...

By the way, the following code can output the polyhedron to OFF format to the screen (from the example 'polyhedron_prog_cut_cube.cpp'):
    std::cout << P;

how to modify the code to let it output to a file 'filename' with the definition:
char *filename;

Use ofstream. Cf for example http://www.cplusplus.com/doc/tutorial/files/

Guillaume

Thanks

---

Date: Tue, 24 Jan 2012 08:28:50 +0100
From:
To:
Subject: Re: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?

Hi Guillaume,

Thank you very much for your kindly reply. Now the problem is solved. I should modify the code like this:

Perfect.

class Build_triangle : public CGAL::Modifier_base<HDS> {
public:
    int nVertices;
    double *Vertices;
    int nTri;
    int *Tri;
    Build_triangle(int nVertices0, double *Vertices0, int nTri0, int *Tri0)
        {
            nVertices=nVertices0;
            Vertices=Vertices0;
            nTri=nTri0;
            Tri=Tri0;
        }


Now my question is: can I pass parameters as a more simple and understandable way, just like the 'Fortran' subroutine?

What do you mean by "more simple and understandable way" ?

Thanks

---

From:
To:
Date: Tue, 24 Jan 2012 19:02:57 +1200
Subject: RE: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?

Hi Guillaume,

Thank you very much for your kindly reply. I am new to C++ class and the complex operators and don't know how to modify the code to pass the parameters to the operator. Is there any simple way to read the input vertices and facets from other functions to form the polyhedron of CGAL? To let the CGAL do boolean operations, should I do like the example? What's the simplest way? I need to generate polyhedron from CSG and then let CGAL to do the boolean opearations and then output the results to OFF file.

Thanks

---

Date: Tue, 24 Jan 2012 07:09:53 +0100
From:
To:
Subject: Re: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?

The variables nVertices,Vertices,nTri,nTri are parameters of the constructor of your class.
Thus they are not defined in the operator(). You need to define variables in your class in order to store them.
Guillaume

Dear Dr. Loriot,

Thank you very much for your kindly reply. I am trying to study the example 'polyhedron_prog_incr_builder' and tried to modify the file 'polyhedron_prog_incr_builder.cpp' as follows:
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#include <CGAL/Simple_cartesian.h>
#include <CGAL/Polyhedron_incremental_builder_3.h>
#include <CGAL/Polyhedron_3.h>

// A modifier creating a triangle with the incremental builder.
template <class HDS>
class Build_triangle : public CGAL::Modifier_base<HDS> {
public:
    Build_triangle(int nVertices, double *Vertices, int nTri, int *Tri) {}
    void operator()( HDS& hds) {
        // Postcondition: `hds' is a valid polyhedral surface.
        CGAL::Polyhedro n_incremental_builder_3<HDS> B( hds, true);
        B.begin_surface( 3, 1, 6);
        typedef typename HDS::Vertex   Vertex;
        typedef typename Vertex::Point Point;
                double *v=Vertices;
                for (int i=0;i<nVertices;i++)
                    B.add_vertex( Point( *v++, *v++, *v++));
                for (int i=0;i<nTri;i++)
                {
                    B.begin_facet();
                     B.add_vertex_to_facet( *Tri++);
                    B.add_vertex_to_facet( *Tri++);
                    B.add_vertex_to_facet( *Tri++);
                    B.end_facet();
                }
        B.end_surface();
    }
};

typedef CGAL::Simple_cartesian<double>     Kernel;
typedef CGAL::Polyhedron_3<Kernel>         Polyhedron;
typedef Polyhedron::HalfedgeDS             HalfedgeDS;

int main() {
    ; Polyhedron P;
        int nVertices=3;
        double Vertices[]={0, 0, 0,1, 0, 0,0, 1, 0};
        int nTri=1;
        int Tri[]={0,1,2};
    Build_triangle<HalfedgeDS> triangle(nVertices,Vertices,nTri,Tri);
    P.delegate( triangle);
    //CGAL_assertion( P.is_triangle( P.halfedges_begin()));
    return 0;
}

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////


The following errors displayed:
1>------ Build started: Project: polyhedron_prog_incr_builder, Configuration: Debug Win32 ------
1>Build started 2012/1/24 11:50:26.
1>InitializeBuildStatus:
1>  Touching "polyhedron_prog_incr_builder.dir\Debug\polyhedron_prog_incr_builder .unsuccessfulbuild".
1>CustomBuild:
1>  All outputs are up-to-date.
1>ClCompile:
1>  polyhedron_prog_incr_builder.cpp
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(16): error C2065: 'Vertices' : undeclared identifier
1>          D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(10) : while compiling class template member function 'void Build_triangle<HDS>::operator ()(HDS &)'
1>          with
1>          [
1>              HDS=HalfedgeDS
1>          ]
1>          D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(41) : see reference to class template instantiation 'Build_triangle<HDS>' being compiled
1>          with
1>          [
1>              HDS=HalfedgeDS
1>          ]
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(17): error C2065: 'nVertices' : undeclared identifier
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(19): error C2065: 'nTri' : undeclared identifier
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(22): error C2065: 'Tri' : undeclared identifier
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\polyhedron_prog_incr_builder.cpp(23): error C2065: 'Tri' : undeclared identifier
1>D:\CGAL\CGAL3.9\CGAL-3.9\examples\Polyhedron\poly hedron_prog_incr_builder.cpp(24): error C2065: 'Tri' : undeclared identifier
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:02.53
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========


Could you please help me to check the problem?



Thanks

> Date: Wed, 18 Jan 2012 11:55:11 +0100
> From:
> To:
> Subject: Re: [cgal-discuss] What's the minimal requirement to use the Constructive Solid Geometry (CSG) module of CGAL?
>
> CGAL cannot handle directly cylinders but only discrete polyhedral models.
>
> See the documentation of Nef package for more details:
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html
>
> Sebastien.
>
> On 01/18/2012 10:41 AM, Zhanghong Tang wrote:
> > Dear Dr. Loriot,
> >
> > Thank you very much for your kindly reply.
> >
> > My requirement is as follows:
> > 1) read the geometries to do the operations;
> > for example, two cylinders with both radius 1 and length 10, the center
> > of top and bottom facet of two cylinders are:
> > cylinder 1:
> > top facet: (0,0,5)
> > bottom facet: (0,0,-5)
> > cylinder 2:
> > top facet (5,0,0)
> > bottom facet: (-5,0,0)
> >
> > 2) find the 3D Boolean operations of input objects and output the
> > presentation by OFF file format.
> > for example, find the unite of two crossed cylinders and output the
> > presentation by OFF file format.
> >
> >
> > How to implement this with mimimal code?
> >
> >
> > Thanks,
> > Zhanghong Tang
> >
> >
> > P.S.:
> > I notice that the mesher 'NetGen' takes the CSG format as its input
> > file, however, it can't handle the simplest example (it works when the
> > radius of two cylinders are not equal), I guess that the CGAL can handle
> > it easily.
> >
> >
> >
> > > Date: Wed, 18 Jan 2012 08:25:30 +0100
> > > From:
> > > To:
> > > Subject: Re: [cgal-discuss] What's the minimal requirement to use the
> > Constructive Solid Geometry (CSG) module of CGAL?
> > >
> > > Zhanghong Tang wrote:
> > > > Dear all,
> > > >
> > > > I would like use the CSG module of CGAL, what's the minimal
> > requirement
> > > > to use this module? I want to build it to a blockbox with CSG module
> > > > data input and another format data output (for example, piecewise
> > linear
> > > > complex format, Geomview's polyhedral file format (OFF)), which files
> > > > should I select to compile and is there any interface to use this
> > module?
> > > >
> > > > Thanks,
> > > > Zhanghong Tang
> > > >
> > > Your question is not clear to me. Could you explain what you are looking
> > > for exactly?
> > &g t;
> > > For 3D Boolean operations, you need to use Nef_3:
> > >
> > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3/Chapter_main.html
> > > For simple polyhedron manipulation, you can use Polyhedron_3:
> > >
> > http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Polyhedron/Chapter_main.html
> > >
> > > Sebastien.
> > > ;
> > > --
> > > You are currently subscribed to cgal-discuss.
> > > To unsubscribe or access the archives, go to
> > > https://lists-sop.inria.fr/wws/info/cgal-discuss
> > >
>
>
> --
> You are currently subscribed to cgal-discuss.
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>

-- 
===================================================================
Guillaume DAMIAND

CNRS, LIRIS  UMR 5205
Université Claude Bernard
Bâtiment Nautibus (710)
43 Boulevard du 11 Novembre 1918
69622 Villeurbanne Cedex (France)
-------------------------------------------------------------------
Phone: +33 (0)4.72.43.26.62               Fax: +33 (0)4.72.43.15.36
Mail: 
===================================================================

-- 
===================================================================
Guillaume DAMIAND

CNRS, LIRIS  UMR 5205
Université Claude Bernard
Bâtiment Nautibus (710)
43 Boulevard du 11 Novembre 1918
69622 Villeurbanne Cedex (France)
-------------------------------------------------------------------
Phone: +33 (0)4.72.43.26.62               Fax: +33 (0)4.72.43.15.36
Mail: 
===================================================================

-- 
===================================================================
Guillaume DAMIAND

CNRS, LIRIS  UMR 5205
Université Claude Bernard
Bâtiment Nautibus (710)
43 Boulevard du 11 Novembre 1918
69622 Villeurbanne Cedex (France)
-------------------------------------------------------------------
Phone: +33 (0)4.72.43.26.62               Fax: +33 (0)4.72.43.15.36
Mail: 
===================================================================